1. Field of the Invention
The present invention relates to a voltage control circuit for an endoscope, and especially relates to a voltage control circuit including a voltage step-up circuit for a light source for illuminating a subject, and so on.
2. Description of the Related Art
A light source for illuminating a subject is sometimes provide at a tip of a scope of an endoscope, for observing a dark subject inside a body. As a light source, an LED is known. In the case where a battery for driving the light source is used, a voltage step-up circuit is also generally used. This is because a high voltage is required for stabilizing the current supplied to an LED especially if the battery voltage has changed, or for increasing the current supplied to the LED for increasing brightness of the illuminating light. Further, the amount of current supplied to the LED for illumination is controlled by monitoring and feeding back the current.
Generally, in the case where an LED for illumination is provided at the tip of a scope of a portable endoscope, the voltage control circuit for the voltage step-up circuit is located apart from the LED. When a portable endoscope is manufactured, each of the voltage control circuit and the LED is built separately, and after being built, they are connected to each other. Therefore, a disconnection between the circuit and the LED, such as a soldering error on lead wires, may occur. Further, the tip of a scope is required to be small and the space for installing the LED is small, therefore, a connecting error when installing the LED may also occur.
When an error occurs with the LED for illuminating a subject, such as a disconnection error, feeding back the current becomes impossible and the step up circuit becomes uncontrollable. Therefore, a large excess voltage being much higher than the required level, may be generated. In this case, peripheral elements may be broken when the excess voltage level is higher than the tolerance level of the elements.